This invention relates to tufting machines and more particularly to a high speed tufting machine having an adjustable eccentric drive for varying the needle stroke and having adjusting means for maintaining the position of the bottom of the stroke, the drive including needle load balancing means.
In the art of tufting one or more rows of yarn carrying needles are reciprocably driven through a base material fed through the machine to form loops that are seized by loopers oscillating below the base material in timed relationship with the needles.
The needles are mounted in a needle bar supported by a needle bar carrier at the end of a plurality of push rods constrained for reciprocatory motion. Conventionally, the push rods are driven by a linkage arrangement connected to a rock shaft which in turn is driven by a lever connected to an eccentrically mounted circular cam, or the push rods are connected to an eccentric strap driven by an eccentrically driven circular cam mounted on a rotating main shaft. An example of the former construction is disclosed in Cobble U.S. Pat. No. 2,977,905, and an example of the latter is illustrated in Ingram, et al U.S. Pat. No. 3,964,407 and in numerous other of the patented art.
When it is desired to change the depth of pile height produced by a tufting machine it is necessary to change the stroke of the needle, and the elevation of the bed plate relative to the loopers, the looper disposition remaining fixed. In conventional machines this involves either changing the eccentric cams which is a very time consuming process, or, in some linkage driven push rod machines, by providing a notch or slot in the rock shaft drive lever and by adjustably locating the connection of the drive cam in the slot. If the slot has a center of curvature coinciding with the geometric center of the cam when the latter is in the bottom dead center position, the bottom position of the push rods will remain fixed. If not, the bottom dead center position will change with changes in the needle stroke. In this latter situation, the bottom dead center will have to be corrected so that the needles and loopers retain their proper relationship, otherwise the loopers will not properly seize loops of yarn from the needles. This may be accomplished by the use of shims between the needle carrier and the needle bar or push rods, or by using needles of different lengths, both of which means are inconvenient and time consuming, the latter also requiring an inventory of needles having varying lengths.
The speed of tufting machines have increased substantially as the tufting art has gradually developed. At very high speeds, e.g., 1,000 rpm and above, the numerous levers and rocker arms of a linkage driven machine tend to wear excessively. Moreover, because of the lever arms used in this construction, there is a large torsional moment exerted on the rocker shaft especially at the top and bottom of the stroke, and this further reduces the useful life of such machines. Additionally, the oscillating movements of the levers in a linkage machine are more difficult to balance than a rotating system.
Because of such difficulties in the linkage drive, most prior art high speed tufting machines utilize rotating drive systems rather than the linkage drive construction. For example, a double eccentric drive is illustrated in Higgins U.S. Pat. No. 3,857,345, wherein one eccentric was mounted within and adjustable relative to the other to change the needle stroke. However, with this construction, when the needle stroke is changed, the timing between the reciprocation of the needles and the oscillation of the loopers is also changed, making it necessary to re-time the machine. It moreover had the same difficulty of repositioning the bottom dead center position and utilized a difficult to adjust cleavage device including a pair of plates that permitted only a minimum number of fixed settings and thus required extremely close tolerances in the production of the machine. Another approach, which is illustrated in Scott, et al U.S. Pat. No. 3,839,972, was to utilize an adjustable crankshaft in which the crank and connecting rods that drive the push rods could be repositioned relatively to the axis of the crankshaft. This proposal, however, had limitations on the amount of stroke adjustability available; the stub shafts comprising the crankshaft had to be changed when greater stroke variations were required so that a number of sets of such stub shafts had to be inventoried. Moreover, because of the large number of stub shafts and crank members required to comprise the crankshaft, wear was excessive and maintenance difficult.
Another difficulty of the prior art, and a major obstacle to attaining a reliable high speed machine, is that of balancing the dynamic loads in the head of the machine. In the aforesaid Scott, et al patent, balancing of the rotating system was attained by utilizing counter weights at ends of the stub shafts to counter balance the eccentricity of the crank. In another proposal, this being for a linkage drive system, a counter balancing rocker shaft is included within the head of the machine and included additional slotted levers driven by eccentric cams out of phase with the needle drive eccentric cams. Again only the rotating and oscillating system was balanced, and not the needle reciprocation system. The additional linkage required for balancing in that system additionally creates further wear and maintenance difficulties.